Blocking Filter, Mini ERFs and Alternatives

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 » Wed Mar 21, 2012 7:12 pm

I don't think it's the same problem... we need the blocking filter to have a large enough bandwidth to allow chasing the doppler shift...as long as the blocking FWHM is around 6-8A it will do its job very well.
( I'm hoping Colin will do a spreadsheet based on the actual blocking filter bandwidth...I think it will show very little sideband passing. Each etalon blocks the other and as long as the blocking filter works within the finesse - there's nothing else left??!!)
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley » Wed Mar 21, 2012 7:39 pm

Hmmm, I keep thinking about this continuum leakage and ways to reduce it... I have to say ever since double stacking I rarely find myself hunting around the doppler shift, I get a pretty decent view of proms and disk simultaneously, my full disk pics are a pretty darn good representation of what i see at the ep. Both etalons are locked down in optimum position and other than a lil' twist of my dew shield which acts like a very fine tuner I find no need to retune - counter intuitive I know; air pressure and temperature et al, but this is the reality of what I find... I do periodically hunt around incase there is a better view, but i seem to have etalon positions nailed.
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by peter drew » Wed Mar 21, 2012 8:51 pm

I've tried double ERF's and double mini ERF's as well as double BF's, no improvement unfortunately, but if you don't try...... :)

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley » Wed Mar 21, 2012 9:05 pm

I've tried double ERF's and double mini ERF's as well as double BF's, no improvement unfortunately, but if you don't try...... :)

fair dinkum, thanks for that Peter! :)
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk » Wed Mar 21, 2012 11:27 pm

The most interesting thing from Joe's spreadsheet was the double peaks from the side bands that leaked through the blocking filter from mis-tuned etalons. I really need to run through the math in that spreadsheet to understand what Joe was doing because his last post differs from my change to the spreadsheet and it is not fair for me to hack his spreadsheet without checking all the math. Joe did a great job and I just hacked in for a quick answer.

As far as the blocking filter specs they are now public knowledge.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 » Thu Mar 22, 2012 2:40 am

Colin,
I thought the bandwidth of the blocking filter in the spreadsheet was slightly greater than the 6-8A we currently have, hence the side band pass?
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk » Fri Mar 23, 2012 1:26 am

It is going to take me a week to go through my notes form the etalon articles and see what spec I have. I know I have Coronado and DayStar's specs.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley » Sun Mar 25, 2012 5:07 pm

I was thinking about blocking filters (again!)...

If the blocking filter is tilted with respect to the optical axis - say as a result of focuser droop / sag, would it's response be slightly blue shifted compared to it's reference value?
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk » Sun Mar 25, 2012 5:31 pm

I was thinking about blocking filters (again!)...

If the blocking filter is tilted with respect to the optical axis - say as a result of focuser droop / sag, would it's response be slightly blue shifted compared to it's reference value?

Yes, When you specify a design you also specify the tilt. I look to see if I have some Dobroski articles. He is the coating [no religion please] for the last 70 years!
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Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk » Sun Mar 25, 2012 7:51 pm

I spelled his name wrong. This is the paper that started the whole mica etalon revolution.

“Mica Interference Filters with Transmission Bands of Very Narrow Half-Widths” by J.
A. Dobrowolski
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Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk » Sun Mar 25, 2012 7:53 pm

Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley » Sun Mar 25, 2012 10:29 pm

Yes, When you specify a design you also specify the tilt.

Hmmmm. Gives us another factor to consider when getting the most out of out Ha systems... :whistle:
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Bob Yoesle » Fri Apr 06, 2012 3:05 pm

I'm nearing completion of my new Ha blocking filter and CaK modules, which will be evacuated and filled with Nitrogen. These are essentially identical units with a sealed inner chamber intended to remove moisture from the primary filter elements and keep thermal stresses to a minimum. Therefore I'm hoping to reduce filter degradation/failure issues as much as possible. They incorporate a "mini ERF" in the form of Baader Red and Blue CCD filters ahead of the enclosed Ha BF assembly and PST/Baader CaK filters (the Ha system also uses a Baader DERF for the SM90's):




I'm trying to obtain optically polished KG5 filters to add in front of the Baader CCD filters.

Here's some of the components - Top row left - completed unit with Blue Baader CCD "mini ERF" - third row left to right - Coronado BF 30, PST/Baader Cak assembly, optical window in cell, bottom right - red Baader CCD "mini ERF." The windows (right) were obtained quite inexpensively from Surplus Shed - 50 mm in diameter and 10 mm thick, both surfaces 1/10th wave ( http://www.surplusshed.com/pages/item/pm1106.html ). Two pairs were AR coated by Majestic ( http://www.majestic-coatings.com/ ) specifically for 656 nm and 395 nm:




The modules will fit inside the AP 2.7 focusers with minimal backfocus issues - machining by Teleskop Service in Germany (very fine workmanship - http://www.telescope-service.com/ ):

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley » Sat Apr 07, 2012 8:00 am

Very professional Bob! :bow:
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver » Sat Apr 07, 2012 10:34 am

A new solar scope brand is born : Bobnado :lol:

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat » Sun Apr 08, 2012 4:32 pm

New to the forum, first want to say thanks! I was SERIOUSLY distressed seeing other sites use monitoring / censorship on random topics. Really ruins the whole forum concept. Sure hope the trend eventually reverses some day and people grow their spines back!!

Anyway, Bob that filter looks great.

I'm interested in making my own "BF25". Since the blocking filter is basically 2 filters, was wondering if it's possible to just screw 2 filters onto the bottom of my camera? If so can you guys point me to the correct filters?

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by jjk » Mon Apr 09, 2012 12:49 am

Mark,

What is the spectral response of your camera? Is it very sensitive to IR > 1400 nm?

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by colinsk » Mon Apr 09, 2012 2:44 am

You can order your own blocking filters. One element is a Notch filter centered on the H-alpha bandpass that matches the Free Spectral Range of your etalon. The out of band blocking is about ND5. The other filter is an ITF and is usually made from silver layers and is designed as a step filter to block IR all the way to IR-C. There are a number of custom filter coaters out there. Some of them will be able to know if there designs are rated for use in solar work.

Somewhere I have the part numbers for the Daystar blocking filters but it is not handy and there is no guarantee that the FSR will match your etalon.
Thank you, Here are some references I have collected.



Etalon Article Part I

Etalon Article Part II

Solar Patents of interest

etatsolarchat

Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat » Mon Apr 09, 2012 6:02 am

You guys talk of replacing the itf with a B+W 489 filter.

http://diglloyd.com/articles/Filters/sp ... W-489.html

Would this followed by a Baader 7nm H-alpha filter work?

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver » Mon Apr 09, 2012 7:50 am

B+W489 is same as KG3 from schott and we saw that it was not enough. Best is KG5 from schott double stack with one other IR cut filter.

Now regarding Ha filter whatever the one you take, they are made for night sky and not enough selective for solar shots.

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by etatsolarchat » Sat Apr 14, 2012 4:51 am

OK, so KG5 filter, then some standard UV/IR blockerd followed by a notch.

Anyone know where I can get KG5, preferably 1.25 or 2in filter?

colinsk, wouldn't the free spectral range be the same for any .7nm etalon? Sorry not an optices engineer, but isn't this just a h-alpha filter with a really tight band of say 1.5nm? Which is why a baader at 7nm won't work?

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver » Sat Apr 14, 2012 6:45 am

For KG5 filter I bought mine here : www.stockoptics.com

Highly professional guys and reactive, but you have to mont them (as soon as it arrive I'll make a picture)

regarding Ha filter, don't forget that we are looking for <1A ones and that 7nm=70A!

I also have one question : ERF is always i front of BF what would happen if I put my new KG filter after it? would it damage it?

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Re: Blocking Filter, Mini ERFs and Alternatives

Post by marktownley » Sat Apr 14, 2012 8:47 am

I also have one question : ERF is always i front of BF what would happen if I put my new KG filter after it? would it damage it?

Yes, The KG5 keeps the thermal load off the blocking filter, if the KG5 was placed behind thermal cycling / loading could damage the blocker...
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by Merlin66 » Sat Apr 14, 2012 8:51 am

It's always best to keep as much energy away from the blocking filter as possible. So, the ERF should be placed somewhere in front of it.

The blocking filter, as Colin said, needs to be "matched" to the etalon performance. We've been lucky to find both the Coronado and Lunt etalons can work with the same blocking filters!
A bandwidth of 6A FWHM centred on the Ha wavelength would be a great start for DIY BF's.
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Re: Blocking Filter, Mini ERFs and Alternatives

Post by DSobserver » Sat Apr 14, 2012 10:37 am

so what about this? :)


looks already better than standard BF

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